1. Field of the Invention
The present invention relates to an engine front structure, and more particularly to an engine front structure equipped with a variable camshaft timing mechanism at a front end of a camshaft of the engine, which is designed to reduce an engine overall length while providing enhanced mounting and supporting stiffness.
2. Description of the Related Art
In an engine for a vehicle, such as a transverse engine designed to be mounted on a vehicle body in such a manner that a crankshaft of said engine is oriented in a width direction (i.e., lateral direction) of the vehicle body, one of the key challenges is how to reduce an outside dimension of the engine in an axial direction of the crankshaft, i.e., an overall engine length. Further, in a design process aiming to reduce the overall engine length, a key task is focused on a fixing structure of an engine mounting bracket for mounting and supporting an engine (including a powertrain unit which is an integrally assembled engine with a transmission unit) relative to a vehicle body, particularly a fixing structure of a mounting bracket for mounting and supporting a front of an engine body relative to a vehicle body. In particular, in an engine equipped with a variable camshaft timing mechanism (also known as “variable cam phase mechanism”), especially a solenoid-controlled type variable camshaft timing mechanism, at a front end of a camshaft of the engine to controllably change a rotational phase of the camshaft so as to change valve timings, the variable camshaft timing mechanism becomes a negative factor causing an increase in overall engine length. Thus, it becomes critical to achieve a shorter overall engine length based on an improvement of an engine front structure including an engine mounting bracket fixing structure.
For example, as a technique of mounting an engine in an engine compartment of a vehicle in a transverse arrangement where a crankshaft of said engine is oriented in a lateral direction of a vehicle body, there has been known a structure for mounting and supporting a front end of an engine body, or one of transverse ends with respect to vehicle, where a camshaft driving force transmission mechanism is arranged, wherein a timing cover fixed to a cylinder head and a cylinder block with a bolt to cover a camshaft driving force transmission mechanism is partially formed with a cutout, and an engine mounting bracket is placed in the cutout and fixed to the cylinder head with a bolt, so that the engine mounting bracket serves additionally as a part of the timing cover in order to facilitate a reduction in overall engine length (see, for example, U.S. Pat. No. 5,743,229).
As a technique for a V-type engine, there has been a structure which comprises a chain case (timing cover) divided into a front chain case and a rear chain case, and an engine mounting bracket divided into a lower bracket and an upper bracket which are integrally connected together with a bolt and assembled to the chain case. Specifically, the lower bracket is formed to extend vertically along a central region of a front surface of the chain case, and an upper bracket has a front end formed as an engine-mount receiving portion attached to an engine mount, and a rearward extension portion extending toward a rear end of the engine to protrude from an upper end of the chain case. The lower bracket is fixed to a cylinder block with a bolt penetrating the front chain case, and the rearward extension portion of the upper bracket is connected to the rear chain case, so as to suppress vibration in a portion of the chain case between banks of the engine. (See, for example, JP 2003-83163A)
As to a structure for mounting and supporting a front end of an engine body in a transverse engine, the above techniques have heretofore been known. Among them, the technique of arranging an engine mounting bracket in a cutout partially formed in a timing cover involves a problem about structural complexity, such as a complicated configuration required for allowing the engine mounting bracket to be used as a part of the timing cover and fixed to an engine body. Moreover, it is not easy to firmly fix the engine mounting bracket onto a front end surface of the engine body which can afford only an extremely limited space therefor due to a camshaft driving force transmission mechanism complicatedly arranged thereover.
In the technique of dividing an engine mounting bracket into a lower bracket fixed onto a front surface of a timing cover and a lower bracket having a front end formed as an engine-mount receiving portion and a rearward extension portion extending toward a rear end of an engine to protrude from an upper end of the timing cover, and integrally connecting the lower and upper brackets together with a bolt, a primary purpose thereof is to suppress vibration in the timing cover, and the lower bracket disposed on the side of the front surface of the timing cover will hinder desirable reduction in overall engine length.